Detection of biological and other analyte molecules is highly useful in diagnosis of medical conditions, evaluation of treatment of medical conditions, for scientific research and other industries. There are currently several approaches to analyte detection. For complex molecules, such as peptides, proteins, RNA, DNA and small molecules, many detection methods rely upon the ability of analyte capture molecules such as specific antibodies or fragments thereof to specifically bind to the analyte of interest. When such analyte-bound capture molecules are made visible (e.g., labelled), the presence of and amount of the analyte can be determined. For example, one form of enzyme-linked immunosorbent assays (ELISAs) is based on the ability of enzyme-conjugated antibodies directed toward the analyte to bind specifically to the analyte of interest. A substrate for the enzyme is then added. Detection of such conjugates, indicating presence of analyte can be accomplished by detecting and quantifying product(s) of enzymatic-derived modification of the substrate. In some of these systems, coloured product(s) are produced, and their detection and quantification can be accomplished using light absorption or emission methods. In certain derivatives of an ELISA, the antibody can be conjugated to a luminescent, fluorescent or radioactive moiety, permitting detection and quantification in the absence of an enzyme.
In other ELISA systems and derivatives of ELISA design, at least two antibodies are used which recognise different epitopes of the analyte (termed “paired”). One of the antibodies takes on the role of capturing the analyte (capturing antibody) and is usually bound to an assay surface. The analyte is brought into contact with the capturing antibody. The second antibody (detection antibody) is then brought into contact with the analyte that is already bound to the capture antibody. The detection antibody is conjugated to a molecule such as an enzyme, or luminescent, fluorescent or radioactive moiety that facilitates detection.
Flow-cytometry-based assays are also currently in use. These assays are based on the detection of labelled particles (including cells) by their passage through a small fluid-filled channel. The appearance of such labelled particles can be detected using laser light and photodetector(s). Such flow-based assays can detect different types of particles based on their size and/or spectroscopic properties, or the presence of a specific marker attached to, or within the particle.